chore: upgrade all GPT model references to gpt-5.4

GPT no longer has separate codex variants (gpt-5.x-codex), unified as
gpt-5.4. Updated ~26 references across 8 files:

- Codex provider presets: default param + 12 vendor configs
- Codex custom template default model
- Universal provider default Codex model (gpt-4o → gpt-5.4)
- OpenCode @ai-sdk/openai: consolidated 7 old models into single gpt-5.4
- OpenCode RightCode: removed gpt-5.2-codex entry
- OMO agent/category recommended models (7 references)
- Stream check default Codex model
- Universal form fallback and placeholder
- Codex form placeholder text

src/components/universal/UniversalProviderFormModal.tsx

@@ -145,7 +145,7 @@ export function UniversalProviderFormModal({
   // 计算 Codex 配置 JSON 预览
   const codexConfigJson = useMemo(() => {
     if (!codexEnabled) return null;
-    const model = models.codex?.model || "gpt-4o";
+    const model = models.codex?.model || "gpt-5.4";
     const reasoningEffort = models.codex?.reasoningEffort || "high";
     // 确保 base_url 以 /v1 结尾（Codex 使用 OpenAI 兼容 API）
     const codexBaseUrl = baseUrl.endsWith("/v1")
@@ -591,7 +591,7 @@ requires_openai_auth = true`;
                     onChange={(e) =>
                       updateModel("codex", "model", e.target.value)
                     }
-                    placeholder="gpt-4o"
+                    placeholder="gpt-5.4"
                   />
                 </div>
                 <div className="space-y-1">